5 hp motor on solar

mike95490 · January 2021

So, someone asked me a question about what inverter would be required to start a 5hp motor.
voltage or phase was not stated, so I'm assuming 240V single phase.
If it was not fully loaded, the data here
https://www.engineeringtoolbox.com/elctrical-motor-full-load-current-d_1499.html
seems like it would be about 25A @ 230V
But how many ganged or stacked inverters would it take to start it up ??

clockmanfran · January 2021

Depends on the Inverter.

Modern HF Inverters, (ie FET driven) have a max headroom rating, get a surge above that headroom the inverter will not function.

Depends on the Motor. Especially if it has a capacitor start.

Transformer types, ie they are very heavy, and i can only speak about 32kg/ 64lbs toroid core transformers, can take huge surges. We know that the 'OzInverter' 6kW to 15kW Inverter can take surge loads up to 50kW for a brief second, give 15kW beyond 15 minutes and run very happy all day at 6kW.

I have been watching Midnite's new HF Inverter progress with some interest to see how they will rate their Inverters for electric motor surge starts.

Dave Angelini · January 2021

Easy, 25 amps starting @230vac = An XWP which can supply 52 amps @ 240 for 60 seconds and specs below for continuous.

I would say it also depends on the load. Just saying it is 5 HP is often meaningless! Especially these days with very marketing intense engineering and less of the plain generic engineering. Pumps and air compressors seem to be all over the map on specs and actual measurement. It is not easy to measure the surge either.

Below is one of the best worldwide. They do not even spec the 1 second surge. I heard it was over 18KW. It starts most anything an offgrid home would require. It can be scaled up to 4 XW if you want more. The only homes that need more offgrid are doing something energy wise that is not standard or normal for a home.

Image: https://us.v-cdn.net/6024911/uploads/editor/3q/ini13acmhcc4.png

MichaelK · February 2021

Dave Angelini said:

Easy, 25 amps starting @230vac = An XWP which can supply 52 amps @ 240 for 60 seconds and specs below for continuous.

I serious doubt that this 25A value is the surge amps. It's more likely to be the running amps. If you assume the surge starting amps is 3-4X higher, you're talking 75-100 starting amps at 230VAC. It's likely that at least 2 XWs in parallel would be required, and I'd want to have 3. The only way to really tell is to get a clamp meter on that motor and actually measure the inrush current. Working with real numbers is always better than educated guesses.

For my own 1hp well pump, my XW+ handles the 9000W starting surge just fine. Running amps is about 9.5A.

BB. · February 2021

And there are always the VFDs (variable frequency drive)--Basically a variable frequency AC inverter--Typically 3 phase.

Most (almost all?) VFDs seem to have square wave outputs... So you want to get an "inverter rated" 3 phase AC motor.

The VFDs can do soft starts, variable speed based on amount of sun, pressure, flow needed, etc.

They seem to have been pretty useful for water pumping and directly connected to solar array (no surge current from solar plans):

Post from 9+ years ago:

Some discussions about VFD (Variable Frequency Drives)... Basically a variable frequency inverter with (typically) three phase output. Used to soft start motors (handy for 3 phase well pumps, or pumps with well head starting capacitor) and can also turn an AC motor into a variable speed motor (very handy for pumping applications).

WELL PUMP and Inverter QUESTION
Wind/solar for large scale pumping etc (out of my depth!)
could use knowledge - using Gould jet pump - transfering from 230vAC to ? DC (new link/thread 10/27/2012)
Help required to design off grid system (information on possibilities to connect "standard VFDs direct to solar panels) (new link 1/13/2013)

And from a new poster, link to solar VFD (looks interesting):

VeichiElectric said:
u really should read this article about solar pumps:
https://www.veichi.org/solutions/water-supply/pump-vfd-or-vsd-for-constant-pressure-water-supply-system.html (updated link -BB 1/1/2019)
In your case I wonder if a solar PV inverter would help or not.

-Bill

1/7/2017:
Dave Angelini said:
Grundfos has been doing solar water pumping for 30 years in the Americas and over the seas

http://us.grundfos.com/about-us/news-and-press/news/Pumped-by-the-Sun.html
They have some really nice plant tours down in the Fresno area of California.

-Bill

mike95490 · February 2021

I think a VFD, with the required snubbers, would be possible, but would require a 3phase motor, would it not ? and they can get some weird circulating currents/voltages requiring the extensive snubbers (which are not often talked about till after the troubles start)

BB. · February 2021

Yes--A three phase motor is pretty much a requirement... An induction motor is cheaper.. .A Permanent Magnet motor is more efficient.

3 phase 5 hp motors should be pretty easy to find vs single phase AC... Helped a friend run multi-HP lathes and mills on single phase 120/240 VAC single phase home based machine shop using a 5+HP 3 phase motor as a "phase converter" (start the phase converter and it generated enough current/voltage for the 3rd leg to run the rest of the 3 phase motors from a single phase service).

-Bill

mcgivor · February 2021

Yes it is possible to feed a VFD with single phase to output 3 phase, in fact it's even possible input DC since it's going to be rectified anyway before being inverted into 3 phase. However one thing worth pointing out is VFD's create voltage spikes which may be in excess if the winding insulation which can cause breakdown of the coating, usually a 600V motor needs to be upgraded to a 1000V insulation to accommodate the transient spikes.

So without knowing the exact motor specifications, can lead to dissapointment, usually not immediately but down the road, my previous dealings with Grundfos drives was an extremely expensive mistake by them, having to replace over 30 motors > 5hp, due to lack of foresight....or ignorance.

Dave Angelini · February 2021

Please MichaelK if you quote me, show the whole context of what I said. I did mention 4 XW's....

A clamp on meter needs to be very good and expensive to capture the surge. Most are on the low side because they can't capture it.

Grundfos is great in North America and takes care of their dealers. If you buy pumps on the internet you should have both eyes wide open, especially if this is for offgrid!

If this is for you Mike, give me a call or text!

mike95490 · February 2021

Not for me - really asking for a friend.
i know about the issues with large VSD and snubbers and filters have to be used ( there is also a big kick back to the AC source, and inverters won't like that) so my inclination is for a 3 ph inverter and a motor exchange for the 230V motor

Dave Angelini · February 2021

Agree Mike, Three phase inversion saves alot of issues in large applications.

The thing to really be super careful with is a large DC motor application. At the bottom of most warranties, it is excluded or a weasel clause is there to limit warranty from large DC kick-back current. Much safer with AC pumps!

MichaelK · February 2021

Dave Angelini said:

Please MichaelK if you quote me, show the whole context of what I said. I did mention 4 XW's....

A clamp on meter needs to be very good and expensive to capture the surge. Most are on the low side because they can't capture it.

Grundfos is great in North America and takes care of their dealers. If you buy pumps on the internet you should have both eyes wide open, especially if this is for offgrid!

If this is for you Mike, give me a call or text!

Well, sorry about that. In your text, your statement as written as "It can be scaled up to 4 XW if you want more", so that did not appear to me that you were suggesting 4 XWs would be needed to run it, just that it was possible.

In terms of a clamp meter, I should have mentioned the words "inrush current" for which I have two meters. A rather expensive Fluke meter, and a far cheaper Chinese Uni-T 216C. Both rated for "inrush", and both measure the same number within 1% of each other.

5 hp motor on solar

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